[Diagnosis of AL amyloidosis in the absence of detectable serum or urinary monoclonal component]

A case of massive amyloidosis without detectable monoclonal Ig component either in serum or in urines on classical electrophoresis and without obvious plasma cell proliferation is reported. Immunohistochemical study of renal and bone marrow biopsies showed that amyloid deposits were specifically stained with the anti-lambda antiserum and that 92% of the plasma cells were also lambda positive. Immunofixation following electrophoretic analysis of serum and urinary proteins exhibited a monoclonal lambda light chain at an advanced stage of the disease. Simple but not routinely used techniques are therefore of great interest to characterize apparently idiopathic amyloidosis which could have therapeutic implications.